1. Field of the Invention
The present invention relates to a semiconductor device employing a WLCSP (Wafer Chip Size Package) and a method of manufacturing the same.
2. Description of Related Art
Semiconductor devices employing WLCSPS are provided by a large number of semiconductor device manufacturers. In a generally provided semiconductor device, a rewire and a sealing resin layer covering the same are formed on a semiconductor chip, and a post passing through the sealing resin layer is provided between an external connection terminal arranged on the surface of the sealing resin layer and the rewire. In recent years, however, the so-called postless structure omitting the rewire, the sealing resin layer and the post has been watched with interest.
A semiconductor device having the postless structure includes a semiconductor chip 101, as shown in FIG. 4. A passivation film 102 is formed on the outermost surface of the semiconductor chip 101. A wire 103 is formed under the passivation film 102, while an opening 104 partially exposing the wire 102 is formed in the passivation film 102.
A polyimide layer 105 is laminated on the semiconductor chip 101. The polyimide layer 105 covers the overall region of the surface of the passivation film 102, and enters the opening 104. The surface of the polyimide layer 102 is planarized. A through-hole 106 is formed in the portion of the polyimide layer 105 entering the opening 104, to pass through the portion in the thickness direction.
A pad 107 is formed on a portion of the wire 103 facing the through-hole 106. The pad 107 fills up the through-hole 106, and the peripheral edge portion thereof extends onto the polyimide layer 105.
A solder ball 108 is arranged on the pad 107. The solder ball 108 is connected to a substrate pad provided on amounting substrate, so that the semiconductor device is mounted on the mounting substrate (electrically and mechanically connected to the mounting substrate).
The base of the semiconductor chip 101 is made of silicon, for example. On the other hand, the base of the mounting substrate is made of glass epoxy resin, for example. The thermal expansion coefficient of glass epoxy resin is greater than that of silicon. If heat is applied to the semiconductor device and the mounting substrate when or after the semiconductor device is mounted on the mounting substrate, therefore, the mounting substrate extremely extends beyond the semiconductor chip 101, and the solder ball 108 is collapsingly deformed following the mounting substrate. When the temperatures of the WLCSP and the mounting substrate are thereafter reduced, the semiconductor chip 101 and the mounting substrate are thermally contracted, and the solder ball 108 is restored from the deformed state.
When the solder ball 108 is collapsingly deformed, remarkable stress is caused on the portions of the pad 106 and the wire 103 connected with each other. If the solder ball 108 is repetitively deformed and restored, therefore, the pad 107 and/or the portion of the wire 103 connected with the pad 107 may be fractured due to repetitive caused remarkable stress.